JPH031508B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection control device for a unit injector used in a diesel engine.

A diesel engine usually includes an injection pump that pressurizes the fuel to perform fuel injection, a fuel injection pipe that supplies the fuel pumped from the injection pump to a nozzle, and a nozzle that injects the high-pressure fuel. However, there is a unit injector that integrates these, and a fuel injection system in which this unit injector is installed in each cylinder is, for example,
It is proposed in SAEpaper No. 750773.

An example of such a unit injector is shown in the first example.
As shown in Fig. 2, unit injector 1
The camshaft 2, which rotates in synchronization with the rotation of the engine, moves the plunger 5 up and down in the figure via the push rod 3 and the rocker arm 4, thereby increasing the pressure of the fuel in the pressure chamber 6, and pumping this high-pressure fuel. The fuel is introduced into the needle chamber 8 of the nozzle 7, the needle valve 9 is lifted up against the valve spring 10, and the fuel is injected from the nozzle hole 12 of the spray tip 11.

In this case, the fuel injection amount is controlled by a control rack 13 by rotating the plunger 5 about its axis via a plunger bushing 14 (the control rack 13 is interlocked with a governor). That is, by changing the timing at which the upper part of the metering recess 15, which is a spiral groove, communicates with the upper port 16 of the bushing 14, and the lower part of the metering recess 15 communicates with the lower port 17, when the plunger 5 descends. The injection amount is controlled by changing the compression start and end times in the pressure chamber 6.

However, in the case of such a conventional unit injector 1, the injection amount was controlled by a so-called mechanical method (the plunger 5 is rotated by the control rack 13). The injection amount or the injection amount determined by a mechanical injection timing adjustment device or the like can only be changed so that it changes approximately linearly or along a gentle curve (due to the shape of the metering recess 15, etc.).
Therefore, there was a problem in that it was not possible to obtain the optimum injection amount in response to changes in engine operating conditions (rotational speed, output, water temperature, etc.).

Therefore, it is necessary to electrically control this injection amount and always perform appropriate matching for fuel efficiency, exhaust, noise, output, etc., depending on the characteristics of the engine and vehicle, as well as the operating conditions. A unit injector for this purpose has been proposed in Japanese Patent Laid-Open No. 54-50726.

However, in such conventional unit injectors, the supply of high-pressure fuel to the injection nozzle was directly controlled using a solenoid valve (injection pressure was directly controlled). If the pressure is 1000 atm and this pressure acts on the tip of the seat of the valve body of a solenoid valve, even if the seat area is made extremely small with a diameter of about 1 mm, it will take 80 minutes to open the valve.
Requires force of about Kg/ ^cm2 . On the other hand, regarding the response speed of this solenoid valve, when applied to a small high-speed diesel engine, for example, at 4600 rpm, fuel is required to be injected at a maximum crank angle of 40° to 45° before TDC. , this period is approximately
The injection period is 1.6 msec, which is extremely short, and during low-load operation, the injection period must be completed in an even shorter period of about 0.4 msec.

Even if it were possible to obtain a solenoid valve having such a high opening force and fast response speed, it would be expensive. Therefore, there is a problem that such a solenoid valve can only be applied to large diesel engines that are slow in speed and expensive.

Therefore, Japanese Patent Application No. 57-67980 proposes a device in which a valve for measuring the amount of fuel to be injected is provided separately, and this metering valve is controlled by opening and closing a solenoid valve. In this plan, when the solenoid valve opens, the fuel pressure operates the piston, which drives the metering valve to release the fuel pressure in the pressure chamber, and the supply pressure from the fuel supply pump operates the piston. For driving, a certain amount of supply pressure (e.g. 5 to several tens of kg/cm ² ) is required.
is required. Furthermore, in order to improve control characteristics, it is necessary to make the metering valve larger, which in turn requires a larger piston. For this reason, it was still not enough to downsize pistons and poppet valves.

The present invention further improves this idea,
A cam that rotates in synchronization with the engine, a pressure chamber to which fuel is supplied via a fuel supply passage by a fuel supply pump, a plunger that pressurizes fuel in the pressure chamber in response to the cam, and communicates with the pressure chamber. A nozzle that opens at a pressure equal to or higher than the valve opening pressure, a fuel relief passage that communicates the pressure chamber with the low pressure side, and a stepped valve having a small diameter portion and a large diameter portion, and opens and closes the fuel relief passage in front of the small diameter portion. a spring that biases the valve body in the valve closing direction; a back pressure chamber formed on the back surface of the large diameter portion of the valve body; and a part of the high-pressure fuel from the pressure chamber into the back pressure chamber. an orifice that throttles the pressure passage; a valve device that opens and closes the fuel supply passage upstream of the back pressure chamber; and control that opens and closes the valve device based on a signal from a means for detecting the operating state of the engine. It is an object of the present invention to provide a fuel injection control device in which the valve device itself is used only to maintain or release the pressure in the back pressure chamber, thereby reducing the size of the valve device.

The present invention will be explained below based on illustrated embodiments.

FIG. 3 is a schematic configuration diagram of an embodiment of the present invention, in which a plunger 23 is slidably fitted into a cylinder 22 bored in a main body 21 of a unit injector 20. 23
The head is urged upward in the figure by a spring 24 interposed between the head and the main body 21, and the head is in contact with a cam 25 that rotates in synchronization with the engine, and one revolution of the cam 25 Each time the plunger 23 is pushed down, the fuel in the pressure chamber 26 is pressurized.

The pressure chamber 26 communicates with a fuel supply passage 28 that communicates with a fuel tank 39. A fuel supply pump 37, which is installed in the fuel supply passage 28 and rotates in synchronization with the engine, supplies the fuel in the fuel tank 39 to the pressure chamber 26. It is now being supplied to

At the bottom of the main body 21 is a nozzle 27 that injects high-pressure fuel pressurized in a pressure chamber 26 into a fuel chamber (not shown).
is formed.

Specifically, the nozzle 27 includes a needle chamber 27D communicating with the pressure chamber 26 via a fuel passage 29, a needle valve 27C, a spring 27B, and a nozzle hole 27E.
It also consists of a spring chamber 27A,
Spring 27B is normally the needle valve 27C.
is urged downward to close the nozzle hole 27E, but the high pressure fuel in the pressure chamber 26 is transmitted to the needle chamber 27D via the fuel passage 29, and this pressure is applied to the spring 2
When the urging force of the pressure chamber 7B (valve opening pressure of the nozzle 27) is overcome, the needle valve 27C is urged upward to open the nozzle hole 27E and the fuel in the pressure chamber 26 is injected from the nozzle hole 27E.

A fuel relief passage 31 branches off from the fuel supply passage 28 that communicates with the pressure chamber 26 .
A metering valve 35 that opens and closes 1 is provided.

Further, further upstream of the fuel supply passage 28 (on the right side in the figure), a solenoid valve 36 is interposed as a valve device for opening and closing the fuel supply passage 28. When the electromagnetic valve 36 closes, the metering valve 35 also closes as will be described later, so that the high-pressure fuel in the pressure chamber 26 cannot escape to the fuel relief passage 31 and is supplied to the nozzle 27.

The valve body 35A of the metering valve 35 is formed into a stepped shape consisting of a small diameter portion and a large diameter portion, and a seat portion is provided on the front surface (pressure chamber side) of the small diameter portion. On the other hand, a spring chamber 35B as a back pressure chamber is located on the back side of the large diameter portion.
A spring 35C provided in the spring chamber 35B biases the valve body 35A to the left (valve closing direction) in the figure. Further, the valve body 35A is provided with a pressure passage 35D for guiding high-pressure fuel from the pressure chamber 26 to the spring chamber 35B, and an orifice 35E for pressure adjustment is formed on the pressure chamber 26 side of this passage 35D.

Therefore, if the solenoid valve 36 were to open, a portion of the high pressure fuel from the pressure chamber 26 would flow from the pressure passage 35D of the metering valve 35 and the spring chamber 35B to the solenoid valve 3.
6 and escapes to the fuel supply passage 28. At this time, orifice 35E for pressure adjustment
A pressure difference between the front and rear of 5E is generated (the pressure on the spring chamber 35B side after the orifice 35E is
This pressure difference between the front and rear pressure chambers 26 generates a large driving force, which quickly moves the valve body 35A to the right in the figure against the spring 35C, opening the metering valve. open. Here, the biasing force of the spring 35C is determined so as not to impair the driving force due to the differential pressure between the front and rear, and when the metering valve 35 opens, the high-pressure fuel escapes to the fuel relief passage 31, and the fuel pressure that reaches the nozzle 27 opens the valve. It is designed to lower the pressure below the fuel pressure and cut off fuel injection.

Also, when the solenoid valve 36 is closed, the spring chamber 3
The pressure in 5B rises to the same pressure as pressure chamber 26,
The differential pressure across the orifice disappears. In this state, the fuel pressure in the spring chamber 35B acts as back pressure, so a driving force is generated according to the pressure receiving area difference between the front surface of the small diameter part and the back surface of the large diameter part of the valve body 35A, and this force and the applied force in the valve closing direction are generated. In total, the valve body 3
5A to the left in the figure and close the metering valve 35.

The above-mentioned solenoid valve 36 includes a valve chamber 36A, a valve body 36B,
Consists of solenoid 36C, solenoid 36
When C is energized by a signal from the control circuit 40, the valve body 36B closes the valve chamber 36A, and when the energization is removed, the valve opens and the spring chamber 35B releases pressure to the fuel supply passage 28. It is something.

The control circuit 40 includes means for detecting engine operating conditions (for example, a rotation speed sensor 41 that detects the engine rotation speed,
An accelerator sensor 42 that detects the depression angle of the accelerator pedal, and a water temperature sensor 4 that detects the engine cooling water temperature.
3. Crank angle sensor that detects crank angle, etc.)
Based on the detection signal from the solenoid 36C, a signal having a drive pulse width optimal for the engine operating conditions is output to the solenoid 36C, and the solenoid valve 36 is controlled to open and close.

An annular groove 32 formed in the upper part of the cylinder 22 communicates with the fuel tank 39 via a fuel return passage 33, and also communicates with the metering valve 25 via a fuel relief passage 31, and a fuel relief passage that branches from the fuel relief passage 31. 31A to the spring chambers 27A, and excess fuel is transferred to the fuel tank 3.
It's starting to go back to 9.

Further, a pressure regulating valve 38 installed in a passage communicating between the fuel supply passage 28 and the fuel return passage 33 maintains the fuel pressure in the fuel supply passage 28 at a predetermined value, and opens when the pressure exceeds a predetermined value. The fuel is then released into the fuel return passage 33.

The effect of the above configuration will be explained based on FIGS. 3A to 3E.

The fuel in the fuel tank 39 is pre-pressurized by the fuel supply pump 37, and is supplied from the fuel supply passage 28 to the pressure chamber 26 via the open electromagnetic valve 36 and the metering valve 35, and the pressure in the pressure chamber 26 is controlled by the fuel supply pump. 3
7 (see Fig. 3A).
As shown in FIG. 4, the fuel supply passage 28 and the pressure chamber 26 are directly connected to each other by a communication passage 45, and in the meantime, a reverse flow occurs in which the fuel flows from the passage 28 to the pressure chamber 26 side but is closed in the opposite direction. By interposing the stop valve 46, the suction stroke of the plunger 23 can be achieved more quickly.

The plunger 23 is lowered by the cam 25 rotating in synchronization with the engine (FIG. 3B shows the point at which it begins to descend) and pressurizes the fuel in the pressure chamber 26, but at this point the solenoid valve 36 is open. A portion of the pressurized fuel escapes from the orifice 35E, pressure passage 35D, and spring chamber 35B to the fuel supply passage 28 via the valve chamber 36A of the electromagnetic valve 36. For this reason, a differential pressure is generated across the orifice 35E, and the driving force due to this differential pressure is applied to the valve body 35 against the spring 35C.
Drive A to the right in the diagram to open the metering valve 35. When the metering valve 35 opens, the pressurized fuel flows into the fuel relief passage 3.
1, the nozzle 27 does not exceed the valve opening pressure and no fuel is injected.

When the plunger 23 further descends and the solenoid 36C is energized at a predetermined crank angle to close the electromagnetic valve 36, the fuel in the spring chamber 35B has no place to escape, so the fuel pressure in the spring chamber 35B increases, and the orifice 35E Differential pressure disappears. In a state where this differential pressure between the front and rear ends, the fuel pressure trapped in the spring chamber 35B acts as back pressure, so a large driving force corresponding to the difference in pressure receiving area between the front surface of the small diameter portion and the rear surface of the large diameter portion of the valve body 35A is generated. This force moves the valve body 35A to the left in the figure, and closes the metering valve 35 after a predetermined period of time has elapsed since the solenoid valve 36 was closed.

can be done.

This predetermined time is a response delay that occurs in the operation of the valve body 35A, but the spring chamber 35C
The response delay time is shortened by assisting the closing operation.

For this reason, the fuel in the pressure chamber 26 is confined and increases in pressure as the plunger 23 descends, and this high-pressure fuel is transmitted to the needle chamber 27D of the nozzle 27 via the fuel passage 29. When the pressure in the needle chamber 27D exceeds the biasing force of the spring 27B (opening pressure of the nozzle 27) that biases the needle valve 27C downward, the needle valve 27C is pushed upward to open the nozzle hole 27E and the pressure chamber 26 is High-pressure fuel is injected into a combustion chamber (not shown) (see FIG. 3C).

When the plunger 23 further descends, the energization to the solenoid 36C is stopped at a predetermined crank angle, and the solenoid valve 36 is opened, a portion of the high pressure fuel in the pressure chamber 26 is transferred to the orifice 35E and the pressure passage 35.
By escaping through D, a differential pressure is generated between the front and rear of the orifice 35E, and a large driving force due to this differential pressure quickly drives the metering valve 35 open against the spring 35C, allowing most of the high-pressure fuel to escape into the fuel relief passage 31. Therefore, the pressure in the fuel passage 29 quickly decreases to below the opening pressure of the nozzle 27, and fuel injection is stopped (see FIG. 3D).

When the plunger 23 starts rising again after reaching the lowest point, the pressure in the pressure chamber 26 decreases, so the metering valve 35 closes again, but the solenoid valve 36 remains open.
From the solenoid valve 36 to the spring chamber 35B and the pressure passage 3
5D and the orifice 35E to the pressure chamber 26 (see FIG. 3E).

That is, fuel injection is performed from a predetermined time after the solenoid valve 36 is closed to when the solenoid valve 36 is opened.

Therefore, the solenoid 36C that opens and closes the solenoid valve 36
The injection timing and injection amount of fuel injected from the nozzle 27 are controlled by changing the energization timing and energization time depending on the operating conditions.

and a metering valve 3 that directly controls the supply of high-pressure fuel.
The opening/closing drive of No. 5 is opened by the driving force due to the differential pressure across the orifice, and is determined by the driving force and valve closing direction determined by the product of the fuel pressure in the spring chamber 35B and the pressure receiving area difference between the front surface of the small diameter part and the back surface of the large diameter part of the valve body 35A. Since the electromagnetic valve 36 is closed by the sum of the spring forces urging the spring chamber 35B, a large driving force is not required.

Therefore, unlike JP-A-54-50726, in which a solenoid valve is used as a metering valve and requires a high opening force and fast response speed to directly control high-pressure fuel,
The solenoid valve 36 may be small and inexpensive. Also, to some extent (for example, 5 to several 10 kg/cm ² ) for the fuel supply pump.
Unlike patent application No. 1983-67980, which required a supply pressure of
The fuel supply pump 37 may be a low-pressure, inexpensive one;
No piston is required and the configuration is simple.

As described above, according to the present invention, a pressure difference is generated between the front and rear by flowing a part of the high-pressure fuel, and the driving force generated by this pressure difference is used to open the valve body, and the back pressure and the small diameter of the valve body 35A are The valve body is closed by the sum of the driving force determined by the pressure receiving area difference between the front side and the back side of the large diameter side and the spring force biased in the valve closing direction, and the valve device is used to release the pressure in the back pressure chamber. Because I am doing
The valve device may be small and inexpensive, and at the same time, the fuel supply pump may also be low pressure and inexpensive, resulting in an effect of reducing costs.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of the conventional device, and Figure 2 is the
3 is a schematic diagram of an embodiment of the present invention, A to E are diagrams for explaining the functions, and FIG. 4 is a schematic diagram of another embodiment of the present invention. It is. 20... Unit injector, 23... Plunger, 25... Cam, 26... Pressure chamber, 27...
... Nozzle, 28 ... Fuel supply passage, 35 ... Metering valve, 35A ... Valve body, 35B ... Spring chamber,
35D...Pressure passage, 35E...Orifice, 3
6... Solenoid valve, 37... Fuel supply pump, 40...
... Control circuit, 41 ... Rotation speed sensor, 42 ... Accelerator sensor, 43 ... Water temperature sensor.

Claims (1)

[Claims] 1. A cam 25 that rotates in synchronization with the engine, a pressure chamber 26 to which fuel is supplied via a fuel supply passage 28 by a fuel supply pump 37, and a plunger that pressurizes the fuel in the pressure chamber 26 in response to the cam 25. 2
3, a nozzle 27 that communicates with the pressure chamber 26 and opens at a pressure equal to or higher than the valve opening pressure, a fuel relief passage 31 that communicates the pressure chamber 26 with the low pressure side, and a stepped structure having a small diameter part and a large diameter part. A valve body 35A that opens and closes the fuel relief passage 31 at the front surface of the small diameter portion, and this valve body 35A.
a spring 35C that urges the valve in the valve closing direction, and a back pressure chamber 35 formed on the back surface of the large diameter portion of the valve body 35A.
B, a pressure passage 35D that guides a portion of the high-pressure fuel from the pressure chamber 26 to this back pressure chamber 35B, an orifice 35E that throttles this pressure passage 35D, and a fuel supply passage 28 upstream of the back pressure chamber 35B that opens and closes. and a means 41 for detecting the operating state of the engine.
43. A fuel injection control device characterized by comprising: control means 40 for driving the valve device 36 to open and close based on signals from 43 to 43.